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Published online by Cambridge University Press: 26 February 2011
We have employed pump-and-probe techniques coupled to ellipsometry to measure the transient complex index of refraction at 1.064 μm of higly oriented pyrolitic graphite (HOPG) interacting with 20 ps, .532 μm laser pulses. When the laser pump fluence exceeds the threshold value for melting, measurements indicate a substantial decrease of both real and imaginary parts of the index of refraction, thus confirming that molten graphite becomes less metallic. Measurements provide also direct evidence of the insensitivity of our picosecond results to evaporation from the irradiated surface.